This invention relates in general to structural attachment fittings and, more specifically, to a fitting assembly providing connection between composite tubes and other structures.
Advanced composite materials are coming into use in applications requiring very high strength-to-weight ratios. These composite materials comprise very high strength fibers, such as graphite and boron fibers, embedded, often in a unidirectional parallel array, in a matrix material such as a synthetic resin or aluminum. Because of the high price and fabrication limitations, these materials have been primarily used in aerospace applications, sporting goods and other applications where their outstanding physical properties are required.
One potential area in which the high strength and light weight of advanced composites would be valuable is in exploration for oil. Drilling towers, derricks and other equipment must often be taken into uninhabited jungle, desert or mountainous areas far from roads. Presently, it is necessary to build roads at great cost in time and money to bring in this equipment. Much of the equipment is too heavy for airlift by helicopter unless broken down, and on-site reassembly facilities are often non-existent. Much of this equipment, if fabricated from advanced composites could be airlifted in complete, ready-for-use form.
Unfortunately, many of these structures cannot be fabricated from composite materials by conventional methods. For example, these materials cannot be welded, riveted or bent by the methods used for metals. Bolt or rivet assembly is undesirable because of the high localized stresses and the loss of strength due to fiber discontinuity at the fastener holes. Attempts to overcome these problems by joining the elements of the entire structure by bonding at a factory have not been entirely successful. Once assembled, the structure cannot be easily changed, modified or repaired.
Thus, there is a continuing need for improved composite structures and fittings for use in oil well derricks, platforms, etc.